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Ch 6 PHOTOSYNTHESIS

6-1: THE LIGHT REACTIONS. Ch 6 PHOTOSYNTHESIS. Light energy absorbed by pigments in photosystems on thylakoid membrane PS II first, then PS I 1. Sunlight energizes electrons at PSII 2. e - picked up by Primary Electron Acceptor Electrons lost are replaced from water

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Ch 6 PHOTOSYNTHESIS

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  1. 6-1: THE LIGHT REACTIONS Ch 6PHOTOSYNTHESIS

  2. Light energy absorbed by pigments in photosystems on thylakoid membrane • PS II first, then PS I 1. Sunlight energizes electrons at PSII 2. e- picked up by Primary Electron Acceptor • Electrons lost are replaced from water • H2O splitting enzyme splits water H2O  H+ + e- + O2 Energy conversion: light to chemical

  3. 3. e- move down electron transport chain (ETC) to PS I • e- lose energy • Energy used to create H+ gradient in thylakoid 4. Light re-energizes e- at PSI 5. energized e- picked up by NADP+ to make NADPH Energy conversion: light to chemical

  4. Compound that can accept a pair of high energy electrons and transfer them along with most of their energy to another molecule Ex.) NADP+ Carrier Molecule

  5. NADP+ NADPH A: this traps sunlight in chemical form Q: What does this do?

  6. Light rxn creates H+ gradient inside thylakoid • Concentration • higher inside thylakoid • Lower in stroma • H+ move through ATP synthase to generate ATP Energy Conversion: light to chemical

  7. To make some ATP • To make NADPH • Which will be used to make sugar What’s the point of the light reaction?

  8. NADP+ = nicotinamide adenine dinucleotide phosphate • RuBP = ribulosebiphosphate • 3-PGA= 3-Phosphoglyceric acid • G3P = glyceraldehyde 3-phosphate Why all the acronyms???

  9. These reactions don’t require light, therefore these reactions are called Light – independent reactions The Calvin Cycle

  10. 2nd set of reactions in photosynthesis In stroma Plants use energy stored in ATP and NADPH to make sugars The Calvin Cycle

  11. Incorporation of CO2 into organic compounds • 3CO2 must enter cycle to make a 3Carbon sugar • Need 3 C to make a 3-carbon sugar. • How many 3-carbon sugars are needed to make a sugar like glucose? Glucose is C6H12O6. So we need two 3-carbon sugars to make one 6-carbon sugar like glucose. So… it takes two cycles through the Calvin cycle to produce one 6-carbon sugar. Carbon fixation

  12. Fructose Galactose These sugars all share the chemical formula C6H12O6. What other 6-carbon sugars are there?

  13. CO2 combines with Ribulosebiphosphate (RuBP), a 5C molecule (What is 1 + 5?) -Resulting 6C molecule is unstable and breaks in half (6/2=?) forming a 3C molecule 3-PGA • 3-PGA converted into G3P using energy from NADPH and ATP Calvin cycle

  14. 3. One G3P leaves cycle -is used to make organic compounds like glucose 4. Remaining G3P molecules are converted back into RuBP using ATP Calvin Cycle

  15. Plants that live in hot & dry places fix carbon in different ways • Plants lose water rapidly • Water lost through pores on leaves called Stomata • CO2 and O2 also move through these pores Alternative pathways

  16. C4 pathway Stomata stays closed during hot parts of day Corn, sugar cane, crab grass (tropical environments) CAM pathway Stomata only open at night Pineapple, cactus Alternative pathways

  17. Light intensity- increases rate of photosynthesis up to a point • CO2 levels- increases rate up to a point • Temperature- increases rate to a point, then drops • Necessary proteins are destroyed at high temps Factors that influence photosynthesis

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